For many years, the electrical cable industry has had the benefit of cable ties to encircle and ensnare groupings of conductors. Applicant's U.S. Pat. Nos. 3,022,557 and 3,047,945, now expired, respectively show examples of cable ties and tensioning apparatus for use in assembling cable ties and conductor groupings. As shown in these patents, cable ties are typically molded plastic members having a head portion and a tail portion extending from the head portion to a free end. The head portion typically includes a pawl member extending into a tail portion passage extending fully through the head portion. The tail portion is routed about the conductors to be ensnared and has serrations on one or both outer surfaces thereof designed to pass by the pawl member under the pulling pressure of a person or a pulling tool, the pawl retentively engaging the serrations to form a cable tie loop tightly encircling the conductors.
In more recent years, the benefit of cable ties has spread to optical conductors, i.e., optical fibers. In such applications, however, there is concern for binding pressure of the cable ties interfering with signal transmission through the optical conductors. The use of the customary cable tie and tensioning device is problematic in this respect, placing such pressure on the optical conductors as to change characteristics thereof and interfere with desired signal transmission therein.
To overcome this problem, the industry has looked to so-called “hook and loop” type fasteners, currently sold under brand names such as GET-A-GRIP, Velchro and Aplix, all of which are registered trademarks.
U.S. Pat. No. 6,484,371 B1 discloses forms of hook and loop fasteners and indicates difficulties attendant on hook and loop fasteners theretofore known.
One such difficulty is referred to as “notch sensitivity”, i.e., a pronounced tendency to tear in one or more directions when a base film of the fastener is notched or nicked, the tearing propagating between rows of hooks.
Other difficulties include the stiffness or flex modulus of the backing material or base film and the thickness of the backing material. This precludes winding the fastener into a tight radius as is required in the bundling of small items, e.g., groups of optical fibers. This also gives rise to the fastener contributing substantially to the overall diameter of the bundled goods, defeating use thereof in areas where space is at a premium.
Another difficulty is that high flex modulus contributes to flagging, i.e., the tendency of the fastener to decouple from itself at the terminal end of the mating surfaces. Flagging also is said to give rise to a cavity in the fastener in which external contaminants can accumulate and contribute to a decrease in the integrity of the coupling after repeated uses.
Further, high flex modulus fasteners also conform more poorly to surfaces that they are wrapped around, making them more prone to slippage, since less of the fastener surface is in contact with the substrate. Moreover, where the fastener conforms so poorly to the surfaces of the bundled goods, the stress applied to the bundled goods is not evenly distributed. In the case of delicate goods, such as optical fibers, this may result in cracking or breaking of the individual fibers or in signal distortion.
Hook and loop fasteners, lastly, due to the bulk thereof, are more costly on a materials basis than conventional cable ties.